Detection of lightning

ABSTRACT

A lightning detector for lightning detection and a lightning detection method, wherein the lightning detector uses at least two separate channels or frequency bands for lightning detection, and wherein the lightning detector is a mobile RF device provided with radio interfaces for at least two communication channels or frequency bands, whereby at least one of which is normally a telecom channel/frequency range and wherein these channels/ranges are used in lightning detection.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional patent application of U.S. patent application Ser.No. 11/250,338 filed Oct. 14, 2005 now U.S. Pat. No. 7,511,467, thecontents of which are hereby incorporated in its entirety.

TECHNICAL FIELD

The present specification discloses a lightning detector, and especiallysuch a lightning detector that uses at least two separate channels forlightning detection. Also a method for detecting lightning is disclosedin this specification.

BACKGROUND

Thunderstorms are a major weather hazard, but are difficult to predict.They can travel at speeds of 20 km/h to 40 km/h, and lightning strokesmay occur more than 10 km in front of the rain clouds and equally somedistance behind the rain clouds. While a lightning stroke is produced bya cloud or a weather front, many of the most dangerous lightning strokesactually occur when no visible clouds are present above as a warning ofa thunderstorm. Thus, a system that warns of possibility harmfulthunderstorms, even if only approximately ten minutes before they becomevisible, can be considered a major safety feature.

There is a large population that would benefit from such a safetyfeature. To some persons, it might provide only a nice-to-know everydayknowledge. To a considerable number of persons, however, storm andlightning originated threats have significant implications in the formof an increased risk, loss of property or even fatal consequences. Alightning alerting system is of particular interest, for instance, forpersons spending much time outdoors, and equally for aviators,navigators or the like. A system providing a warning of lightning evenwhen the weather seems to be perfectly calm and clear may enable aperson to take suitable safety measures in time, for instance seekshelter etc.

From the state of the art, many single-purpose lightning detectors areknown, but they have some disadvantages from a commercial perspective.Scientific lightning detectors, which are used in meteorology, are verylarge and their range is hundreds of kilometers.

Also other high-end lightning detectors using a single radio frequency(RF) band are large and relatively expensive, compared for instance tomobile phones. Moreover, they are usually required to have a specificorientation, for instance standing on a wall or on a desk stand, inorder to gain the required accuracy or directionality. They are thus notwell suited for a truly mobile use. These devices typically have furtherto be positioned in a certain way and held stationary for severalminutes before a reliable detection of a thunderstorm becomes possible.

In addition, there are now existing rather inexpensive low end lightningdetectors which are completely portable in size and which do not requirea specific orientation. These detectors, however, are extremelysusceptible to man-made electromagnetic compatibility (EMC) emissionsand thus tend to cause spurious alarms especially in an urban setting ornear highways

Currently most of commercially available mobile lightning detectorsdetect lightning strokes by measuring the electromagnetic emissioncaused by lightning at very low frequencies (VLF: 3-30 kHz). Inaddition, it has been known for decades that lightning strokes can be“heard” by using a traditional AM broadcast radio receiver, whichoperates at longwave frequencies (150 to 300 kHz), mediumwavefrequencies (500 to 1700 kHz) and shortwave frequencies (SW: 2 to 30MHz). However, numerous publications exist where lightning have beendetected and measured by its emission at HF and VHF frequencies between3-300 MHz and even at higher (UHF) frequencies.

SUMMARY OF SOME EXAMPLES OF THE INVENTION

The present invention proceeds from the consideration, that a lightningstroke is a single flash which produces besides a visual signal and apartly audible pressure signal as well a brief but strongelectromagnetic pulse extending over a wide variety of wavelengths.Typical electromagnetic pulses caused by a lightning stroke cover thefrequencies between 10 Hz and 5 GHz with a peak around 500 Hz, i.e. inthe audio frequency range. At a normalized distance of 10 km, theamplitudes of such pulses range from 107 mV/m to 1 mV/m in a bandwidthof 1 kHz. the strongest signal of the electromagnetic pulse is theinduced electric field caused by the vertical current in the lightningstroke, and this is the parameter that is most commonly measured inlarge-scale distance-bearing devices.

However, due to the complexity of the lightning stroke phenomena, thereare also strong signals in the extremely low frequency (ELF) range of afew hundred Hz or less, and weaker signals extending up to the GHz rangeand above.

It is a well-known fact that the exact characteristics and time spectraof the electromagnetic interference (EMI) signatures are different inthe MHz range that in the kHz and Hz ranges due to the slightlydifferent meteorological mechanisms causing them.

For the purposes of the present invention it is sufficient to note thatat all frequencies of interest, a lightning stroke is accompanied by anEMI pulse that can be identified at a distance of many kilometers.

As a result of the lightning stroke generated EMI pulse, RF channels arebriefly interfered during a lightning stroke in the vicinity. Theimpairment of RF receivers due to an EMI caused by a lightning strokecan be experienced in using an AM/FM radio, TV or over power supplylines in form of statics, clicks, scratches, noise or loss of sound orpicture. Disturbances in RF channels due to a lightning stroke can besensed at very large distances. Specialized and large-scale lightningdetectors are able to detect lightning disturbances, so-called sferics,at a distance of several hundreds of kilometres from a lightning stroke,although these detectors typically operate by measuring the inducedelectric or magnetic field rather than the interferences in an audio orRF signal as one example of the present invention.

Ordinary AM radios are known to suffer from EMI disturbances at adistance up to 30 km or more from a lightning stroke, which can even beheard directly in an audio signal as various clicks. At higherfrequencies than the AM bands the signal is typically much weaker due toboth atmospheric attenuation and different causation mechanisms, but isnevertheless detectable at large distances.

While in known mobile RF devices, such as ordinary mobile phones,electromagnetic interference in received RF signals are eliminatedimmediately by filtering, it is proposed in one example of presentinvention that such electromagnetic interferences in a monitored RFchannel are evaluated. If a detected interference seems to be caused bya lightning stroke, a user of for example a mobile phone can be alerted.An interference can be assumed to be caused by a lightning stroke, forexample, if it exceeds a predetermined threshold value or if it has afrequency spectrum which is characteristic of a lightning stroke. Thelightning detection can be on as long as the RF detection is on.

The present solution thus provides a new security feature that can beimplemented in a mobile RF device, for example a cellular phone.

While in many case, the desire to detect lightning strokes in thevicinity may not be large enough to justify the costs and the difficultyof carrying along a dedicated lightning detector, many people wouldappreciate a low-cost sensing system that could be integrated with adevice that they are already carrying along in any case, especially likea mobile phone. The known art does not provide for such an integrationof a lightning detection as a new functionality in known mobile RFdevices.

It has been found out that lightning detection and ranging feature wouldbe a desired feature e.g. in mobile phones. Sufficient detection rangefor the lightning stroke detection feature in mobile products would beabout 20-30 km. This detection range might be limited to a suitablerange depending on the receiver sensitivity and the expected emissionpower from lightning strokes. FIG. 10 shows in graphical formfrequencies and amplitudes that have been generated by lightningstrokes, as determined by many researchers. The graph according to FIG.10 can thus be used as a guideline to estimate the strength of signalsthat can be expected from lightning strokes at different distances. Inthe graph the distance is normalized to 10 km and the bandwidth isnormalized to 1 kHz. According to the this graph, lightning strokesignals can be detected at least up to 300 MHz.

One example of the present invention is based on the idea that theincoming spectrum generated by a thunderstorm is studied using all ormany available RF channels available in a mobile RF device, such as acellular phone. Because of the many radio interfaces (i.e. hundreds ofchannels in each of the three bands in a tri-band receiver, theBluetooth receiver frequencies, the FM radio including the pilot tonechannel, the Wi-Fi radio local area receiver, the RFID tag reader andeven the RDS and/or DARC receivers) the example of the present inventionprovides a new and feasible method for lightning detection.

Thus according to the first example of the invention, the solution isbased on the use of at least two channels, at least one of which is atelecom channel, for lightning detection.

For the first example of the invention it is therefore proposed that thelightning detector is a mobile RF device provided with radio interfacesfor at least two frequency ranges, whereby at least one of which isnormally a telecom channel, for lightning detection.

In a further example of the present invention, taking into considerationthat the emission from a lightning stroke is a wideband burst, severalchannels or a complete frequency band reserved for telecommunication isused at least to provide a triggering mode receiving maximum energy andthus increasing sensitivity.

According to a still further example of the present invention at leastone of the bands is the FM broadcasting frequency band.

One example of the present invention is to utilize the suitable parts ofa FM radio receiver in lightning detection, and to add a dedicatedlightning detection branch to the receiver.

Some examples of the present invention further include multipleembodiments of modifying an FM receiver to identify and measurelightning strokes. According to theory FM modulation is chosenspecifically for broadcasting in order to minimize statics and cracklingcaused by atmospheric disturbances like lightning. However, if the FMdemodulator, especially the limiter stage, is by-passed and theresulting signal is e.g. AM demodulated, then the disturbanceoriginating from lightning strokes can be analyzed.

Characteristic features of the lightning detector and the method ofdetecting lightning according to one example of the present inventionare in detail presented in the enclosed claims.

The present solution has the benefit that it can provide a portablelightning detector integrated with a mobile telephone. Another aspect ofthe solution is that hardware changes can be minimized, in the methodsby which hardware (HW) changes can be minimized, thus limiting costs andshortening time to market.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the examples of the invention will be described inmore detail with reference to the appended drawings, in which

FIG. 1 presents an operational environment,

FIG. 2 presents auxiliary receiving bands

FIG. 3 presents a block diagram of a single radio implementation.

FIG. 4 presents a flow chart of a single radio operation,

FIG. 5 presents a block diagram of a multi radio implementation,

FIG. 6 presents a flow chart of the multi-radio operation

FIG. 7 presents a block diagram of a receiver with lightning detection,

FIG. 8 presents an alternative block diagram of a receiver withlightning detection,

FIG. 9 presents another block diagram of a modified receiver modulatorwith lightning detection and

FIG. 10 is a lightning data graph, and

FIG. 11 depicts a modified I/Q demodulator, and

FIG. 12 depicts a modified I/Q demodulator with a switch.

DETAILED DESCRIPTION

The basic principle of one example of the invention is to utilize thesuitable parts of a telecom radio receiver in lightning detection, andadd a dedicated lightning detection branch to the receiver.

Lightning strokes emit bursts of pulses detectable on frequencies usedfor broadcast radio. Originally the FM radio broadcasting system wasintroduced because the existing AM radio system was too sensitive tointerference e.g. generated by lightning strokes. The reason for thesensitivity of AM radio to lightning strokes is that interference fromlightning strokes sum with the amplitude modulated signal. Theinterference in amplitude is heard as crackling static in AM radioreceivers. The intensity of the signal emitted by lightning strokes isalso higher on AM broadcast frequencies (near 1 MHz) than the FMbroadcast frequencies (near 100 MHz). Since in FM systems the audiosignal is modulated to the carrier as frequency or phase changes,interference in amplitude does not cause audible crackling or othererrors in the received signal, because as the amplitude is not bearingmodulation it can be limited by a limiter before the FM discriminator orratio detector. However, if the lightning stroke occurs nearby (within acouple of kilometres) of the FM receiver, correlation betweeninterfering noise heard from from for example a battery powered FMreceiver and the lightning flashes can be observed.

But if demodulation is not considered, lightning strokes still emitbursts of pulses detectable on frequencies used for FM radio reception,like the 87.5 to 108 MHz frequency band in Europe and the 88 to 108 MHzband in USA and the 76 to 91 MHZ frequency band in Japan. Since FMmodulation is robust against interference caused by lightning strokes,the interference cannot be heard by using traditional FM radioreceivers. The lightning detection feature require a demodulator workinglike an AM demodulator. As already mentioned, the AM demodulator is verymuch more sensitive to interference caused by lightning strokes. Theadditional lightning stroke detector can be added in parallel with theFM demodulator/receiver. The correct stage where the lightning detectorHW should be added is after the down-conversion mixer and before limiterstage in FM radio receiver.

As can be seen depicted in FIG. 2, a FM stereo broadcast comprises inaddition to the main monophonic FM broadcast 21 additionally asuppressed 38 kHz center frequency and 30 kHz wide subcarrier 23 forstereo audio content and a 19 kHz pilot tone sub-carrier 22 tofacilitate the regeneration of the right and left stereo channels.

To send program content and other data to display equipped radioreceivers another 57 kHz center frequency and 7 kHz wide RDS (Radio DataSystem) subcarrier 24 was later added to most FM broadcasts. A new 32kHz wide DARC (DAta Radio Channel) subcarrier 25 centered around 76 KHzhas additionally been standardized in 1995 by ETSI as ETS 300751.

Currently, the FM channel spacing is 100 kHz in Europe and 200 kHz inUSA. The reception of RDS signal would require a somewhat widerbandwidth than 100 kHz, but it's unclear if channels with RDSbroadcasting have a wider channels spacing also in Europe. In the futureall new FM receivers may be capable of receiving the whole (about 200kHz wide) frequency band containing the RDS and DARC sub-carriers.

The burst of pulses generated by lightning strokes is possible to detectwith a receiver on carrier frequency near to 100 MHz (at least on anempty FM channel). As presented in FIG. 2, the receiving of pulse burstis possible at least if the reception channel is about 300 kHz wide.Narrower bandwidths might be feasible, as well. Depending on the actualimplementation the channel width of FM receiver front-end is about100-200 kHz as presented above.

Since the spectrum of RF emission from lightning strokes is moreintensive on low frequencies, the lower end of FM frequencies is betterthan the higher one. The most feasible FM channels are near to lower endof FM frequency band which is 76 MHz (in Japan), 87.5 MHz (in Europe) or88 MHz (in USA).

Several embodiments of lightning detection using modified FM receiverswill now be described in the following.

An arrangement is depicted in FIG. 7 where the signal 81 or 83 for thelightning detection block 80 is tapped before the limiter 75 becausemost of the lightning noise information would be lost by the amplitudelimiting action in the limiter 75, but the tapped signals 81, 82 in thefigure shown as a typical differential signal like in present daycircuits, is unaffected and still contains information related to thelightning stroke noise.

The FM receiver path from antenna to the discriminator 70, 71, 72, 73,74, 75 and 76 can be considered to be similar to the corresponding pathin a commercial IC sold by Philips as TEA5767.

Embodiment 1

In the first embodiment the FM receiver path from antenna to thediscriminator 70, 71, 72, 73, 74, 75 and 76 has an additionalintermediate output 81 would be between the down-conversion mixer 73 andthe limiter stage 75. The circuit block 74 contains amplification andfrequency selection means. The intermediate signal containing theamplitude information caused by the RF emission from lightning strokesis input via 81 to a lightning detection specific block 80. In thisimplementation alternative the detection bandwidth would be similar tothe selected FM channel (100-200 kHz).

Embodiment 2

In another embodiment alternative the intermediate output 82 is arrangedimmediately after the low-noise preamplifier 72. In this alternative thedetection bandwidth would be the whole FM band (e.g. 87.5-108 MHz inEurope) as passed on by the FM band filter 71 between the antenna 70 andthe low noise preamplifier 72. This alternative embodiment couldadvantageously be used in trigger mode for lightning-like signals. Thereceived power on the band could be measured with a wideband powerdetector and if fast wideband signals (like lightning strokes) exist inthe signal, a more accurate detection could be started e.g. on one ofthe FM channels.

One possibility is to have an additional separate down-conversion mixerfor the lightning detector. This is indicated as 83 in the lightningdetection block 80 of FIG. 8 and the arrangement would allowsimultaneous lightning detection and FM radio reception on different orthe same FM bands.

However, this kind of implementation requires additional HW dedicatedfor the lightning downconversion which would not be needed if the signal82 is tapped after the downconversing mixer 73 like in the firstembodiment.

Embodiment 3

Lightning detection can advantageously take place in an empty FMchannel. Finding of an empty FM channel is easy using the conventionalFM stereo receiver path. The found empty channels can be used forlightning detection. As presented above, lightning detection on an emptyFM channel would require an intermediate output after down-mixer in theFM receiver. The reason for this is that the FM modulated signal islimited to a low amplitude before frequency demodulation in the FMdiscriminator 76. The limiting extracts the signal caused by RF emissionfrom a lightning stroke and after the limiter no lightning detection ispossible. In addition, if no FM signal exists on the FM channel, thenoise of FM demodulator increases significantly. Merely this incrementof noise makes detection of lightning hard although it otherwise wouldbe possible from the demodulated but empty FM channel. For lightningdetection the FM discriminator should be replaced with an AM detectorsensitive to amplitude changes.

On an empty FM channel the whole channel can be utilized. In case of abasic FM stereo receiver the Rx channel is +/−53 kHz wide around thecarrier frequency. In case of stereo FM RDS receiver the Rx channel is+/−60 kHz wide and in case of a DARC compatible FM receiver the channelwidth is +/−92 kHz around the carrier center frequency.

Embodiment 4 Detection while FM Reception is Active

The optimum situation, from the point of view of the user, is toimplement a lightning detection feature that simultaneously permits bothlightning detection and reception of a FM radio broadcast. But the FMradio signal is continuous and therefore there is no gaps in thetransmission so if the lightning stroke is weak (for example due to adistant stroke), it might be difficult to detect lightning strokes on anFM channel where radio transmission is active, but this embodiment canstill be used for lightning alerting or triggering purposes.

Some ideas for implementation now follows:

a) Lightning detection can be done on the basis of the signal receivedaround the 19-kHz sub-carrier. Current stereo FM broadcasting leaves thechannel between 15-23 kHz empty except the narrow 19-kHz pilotsub-carrier. These frequency portions around the pilot carriers areavailable on every FM channel.b) One alternative is to detect lightning strokes simultaneously with FMstereo reception on an inactive RDS or DARC channels. In addition, ifRDS and/or DARC contains gaps in transmission, the gaps could be used todetect lightning strokes simultaneously with stereo FM reception.c) It is possible to detect interference simultaneously when receiving aFM transmission. If for example detectable interference exists e.g. onthe channel around 19-kHz pilot sub-carrier, a more accurate lightningdetection mode could be activated. The more accurate detection would bemade on an empty FM radio channel and could contain distance estimationas well. The trigger mode would only detect lightning-like interference.d) If the reception bandwidth can be arranged to be wider than the 100kHz respective 200 kHz bandwidth needed for of a FM broadcast channel,the lightning detection or lightning triggering can be performed betweenthe FM channels because in practice, neighboring channels are seldomused.

Embodiment 5 Utilization of AGC (Automatic Gain Control)

One idea that is feasible is the utilization of the AGC stage of an FMreceiver for lightning detection. AGC functionality is widely used in FMreceivers (see e.g. the Philips TEA5767 FM receiver). If some of theloops in the AGC circuitry can be made sensitive to a signal componentgenerated by lightning strokes, it might be possible to get a sufficientintermediate signal directly from the AGC stage and no othermodifications are needed in FM receiver stage. However, the timeconstant of the AGC circuit bust be tuned short enough to enabledetection of the short pulses caused by lightning strokes.

External capacitors are often needed in implementation of an on-chip AGCstage and therefore only small modifications to the integrated circuitis needed if the intermediate output can be connected to these externalcapacitors. If pulse detection is feasible, the idea can be used atleast for the triggering mode if more accurate detection is notpossible. Another measurement mode could be implemented for distanceestimation etc.

Embodiment 6 Multi-Mode Detection

In the simplest mode, only one radio (i.e. FM radio receiver) isutilised during the detection. FIG. 3 depicts such a system 34comprising a single radio 31. Different modes are used by the processor33 to optimize power consumption. For example, in the less powerconsuming mode perhaps only the front-end is turned on in the powersaving mode and analog peak detection is used to trigger more powerconsuming components as ADC and processor, like presented above in theimplementation example 2. Between full operating lightning detection andtriggering mode, there can be a monitoring mode that will decide whetherthe device should switch to lightning measuring mode or go back totriggering mode. An example of an operational chart of operation for thesingle radio implementation is presented in FIG. 4. During the low powermonitoring mode in step 41 the received signal is continuously monitoredin step 42 and if lightning activity is detected a more power consumingbut more precise detection mode is selected in step 43 and if in step 44the analysis meets the criteria for user alerting, this is done in step45, otherwise the system returns to the low power monitoring mode instep 41.

Another possibility is to use two separate radios in a system 53depicted in FIG. 5, either using a common antenna or separate antennas,a main lightning detection radio 51 and another radio 52 that is usingless power, but is less accurate. In this case, the less power consumingradio 52, e.g. RFID tag reader, is used in triggering mode. An exampleof an operational chart of operation for the multiple radioimplementation is presented in FIG. 6. Low powered monitoring of anempty channel takes place in step 61 using AM detection advantageous forlightning detection, When lightning energy is detected by the AMdetector in step 62 the processor 52 controls the other radio in step 63to analyze the received signal and if the analysis in step 64 meets thecriteria for user alerting, this is done in step 65, otherwise thesystem returns after a predetermined time to the low power monitoringmode in step 41 using the radio 51.

Embodiment 7 Energy-Optimized, Multiple-Mode Multiple-Band, TriggeringSystem for Lightning Detection

A mobile device able to work in at least two modes, each mode capable ofsome level of lightning detection and ranging is described in known art.These modes can utilise the same radio in a different way or utiliseseparate radios for the various modes. This embodiment comprises acontroller 33, 53 in FIG. 3 respective FIG. 5 which is able to keep thedevice in a low-energy “triggering” mode as much as possible, onlylaunching more power consuming modes when triggered. The controllerselects an optimal radio for a semi-passive low-energy-consumption“triggering” mode: the radio simply responds to all EMI pulses thatcould be related to lightning, but makes no further processing. Instead,when triggered, it opens a “monitoring” mode that can consume moreenergy. This can be a different radio, or the same radio operating in adifferent mode. The monitoring mode evaluates EMI pulses moreaccurately. If it detects an event that has a good chance of being alightning event, only then the “measuring” mode is opened. In this mode,the full processing power is used to detect, identify, and evaluatepossible lightning strokes to the best possible accuracy. In a preferredembodiment, the measuring mode opens more than one of the possibledetection channels.

Note that the mode structure can be either simpler or more complex thanthe one described. In the simplest possible mode, there is only atriggering mode (e.g. RFID) which launches the measuring mode directly.In more complex systems, there may be multiple triggering & monitoring &measuring modes.

The number of possible radio receiver combinations that might bepossible to use in lightning detection is relatively large. Below is ashort list of the possible combinations and estimations how power couldbe saved by using trigger and detection modes separately.

Using Audio+AM/FM

Most of the current commercial lightning detectors operate on relativelylow frequencies i.e. on audio frequencies from hundreds of Hz to 10-100kHz. Some commercial or research detectors operate also on AM or FMfrequencies. It seems very probable that a good and power efficientlightning detector implementation would simultaneously utilize receiverson audio and AM/FM frequencies especially in devices where AM and/or FMreceiver exists anyway. The detection on multiple frequency bands (farenough from each other) gives better estimations about distance tolightning strikes. On the other hand, if several receivers are activesimultaneously the power consumption is of course higher. Therefore itis advantageous to have separated triggering and measuring modes.Depending on the current consumption and sensitivity of differentreceivers and portions the triggering receiver may be either audio, AMor FM receiver. For example, a peak detector implemented on audiofrequency path could be the trigger which activates more accuratedetection on several frequencies.

Using RFID:

As previously mentioned, a modified RFID reader could be used as atriggering device to launch a more accurate lightning detection mode.The RFID reader front-end could be modified for example by adding afrequency selective (5-10 kHz) peak-detector. If some predefinedpeak-level exceeds in triggering mode, the measuring mode would belaunched. The measuring mode could include for example using of audioand/or AM/FM based detection and ranging.

Detection Based on Detection on Frequencies 100 MHz and Above:

According to lightning related literature, depending on the phase andtype of a lightning, electromagnetic emission on relative highfrequencies exists. For example, cloud-to cloud lightnings emit signalon GHz frequencies. Additionally, the stepped leader phase of cloud toground lightnings emit high frequencies. Thus, the detection of emissionon higher frequency could be an indicator for increased lightningprobability which could trigger measurement mode. However, as can beseen from the graph depicted in FIG. 9, the power of emission on GHzfrequencies is relatively low and therefore sensitivity of triggeringreceiver should be high.

Man-Made EMC Elimination

Further, the so-called man-made noise elimination may be implemented asa software function that is capable of finding fixed interval peaks inthe received signal and filtering them away. This can be implements forexample by keeping a record of detected intervals and analysing if somespecific intervals appear constantly or cover constantly a certain timeperiod. During the man-made noise the lightning detection can beswitched off.

Using Other Auxiliary Receivers

While the above description is mainly related to the use of FM radio inthe lightning detection, also other frequency ranges, i.e. hundreds ofchannels in each of the three bands in a tri-band receiver, theBluetooth receiver frequencies, the FM radio including the pilot tonechannel, the Wi-Fi radio local area receiver, the RFID tag reader andeven the RDS receiver can be used.

Using I/Q Branches Unsymmetrically

During reception a signal is typically decoded in a demodulator havinginphase and quadrature branches. These branches are made as symmetricalas possible in traditional receivers in order to minimise errors in thecancellation of the local oscillator signal. For example, the frequencyand gain are traditionally the same for both branches. However, in theelectromagnetic signature of a lightning strike lightning there is nophase information, so lightning detection can be made on the basis ofonly signal magnitude and envelope shape. Therefore it is possible touse the I and Q branches of the receiver separately i.e. the receivercan be modified so that the lightning detector utilizes two channelswhich detect different characteristics of the signal.

Using Different LO Frequency in I/Q Branches

A typical dual branch I/Q demodulator can be arranged in one mode to beused to detect lightning strikes on different frequencies while inanother normal mode functioning traditionally, especially if thearrangement does not affect the precise branch balance in this normaluse. For example, and as depicted by FIG. 10, the local oscillatorfrequency to one branch can be changed using digital means, e.g. using aprogrammable counter 101 that adjusts the local oscillator signal. Usingthe phase and quadrature branches of an I/Q demodulator in this way isequivalent to having two different radio receivers operating ondifferent frequencies and is a very cost effective way to implementsimple multiple receivers.

Using Different Gain in I/Q Branches

A typical dual branch I/Q demodulator can further be arranged in a onemode to operate with different gain on each branch while in another modeit functions normally for broadcast reception. This is depicted in FIG.11 where the control means 111 and 112 adjusts the gain in the in-phaserespective the quadrature branches. Because the amplitude of lightningstroke signals shows huge variations, this is a very effective way toimplement far and near detection of lightning strikes and this methodcan also advantageously be used for triggering in the previouslydiscussed monitor mode.

Using One Branch in Baseband Mode

FIG. 12 depicts how one branch can be used in baseband mode without anyfrequency conversion and is very efficient to receive lightning strikes,which according to the graph depicted by FIG. 9 is rich in low frequencyenergy, especially at low frequencies 91. A suitable longer wire antenna121, for example a headset wire antenna, can advantageously be used thisway. The use of the amplification, filtering and data conversion 126means in the branch can thus very cost effectively be used to advantageif a switch 124 is arranged for a signal from the front end 122 ordirectly from the antenna is switched into the amplification andfiltering path by the switch 124 to be converted by the analog todigital converter 126 in FIG. 12. A suitable gain for the amplificationand filtering path when used for this purpose can be selected using thecontroller 125.

It is obvious to a person skilled in the art that different embodimentsof the invention are not limited to the examples described above, butthat these may be varied within the scope of the enclosed terms.

1. An apparatus comprising: a telecommunication radio receiverconfigured to receive a telecommunication frequency band signal andprovide a triggering mode in response to a detection of a widebandinterference burst; a frequency modulation radio receiver configured toreceive a frequency modulated frequency band signal; a processorconnected to the telecommunication radio receiver and the frequencymodulation radio receiver, and configured to cause the apparatus todetect interference originating from lightning by performing: inresponse to the triggering mode, by-passing a limiter stage of thefrequency modulation radio receiver to provide a resulting signal;demodulating the resulting signal using amplitude modulationdemodulation; and detecting the interference originating from lightningbased on the demodulated resulting signal.
 2. The apparatus of claim 1,further comprising a frequency modulation demodulator and a lightningdetection block being arranged in parallel.
 3. The apparatus of claim 2,wherein the lightning detection block is placed after a down-conversionmixer and before the limiter stage in frequency modulation radioreceiver.
 4. The apparatus of claim 1, wherein the apparatus has anintermediate output after down-mixer in the frequency modulation radioreceiver and further wherein the processor is configured to cause theapparatus to perform: using an empty frequency modulation channel forlightning detection.
 5. The apparatus of claim 1, wherein the processoris configured to cause the apparatus to perform: receiving frequencymodulation radio signals simultaneously with the lightning detection. 6.The apparatus of claim 1, wherein the processor is configured to causethe apparatus to perform: using an automatic gain control stage of afrequency modulation radio receiver in the lightning detection.
 7. Theapparatus of claim 1, wherein the processor is configured to cause theapparatus to perform: using an in-phase and a quadrature branch of thetelecommunication radio receiver for providing the triggering mode. 8.The apparatus of claim 7, wherein the processor is configured to causethe apparatus to perform: using different local oscillator frequenciesin the in-phase and the quadrature branch.
 9. The apparatus of claim 7,wherein the processor is configured to cause the apparatus to perform:using different branch gains in the in-phase and the quadraturebranches.
 10. The apparatus of claim 1, wherein a telecommunicationradio receiver comprises a radio frequency identification tag.
 11. Amethod comprising: detecting lightning in an apparatus comprising atelecommunication radio receiver and a frequency modulation radioreceiver; receiving a telecommunication frequency band signal using thetelecommunication radio receiver; providing a triggering mode by thetelecommunication radio receiver, in response to detecting a widebandinterference burst; receiving a frequency modulated frequency bandsignal using the frequency modulation radio receiver; by-passing alimiter stage of the frequency modulation radio receiver to provide aresulting signal in response to the triggering mode; demodulating theresulting signal using amplitude modulation demodulation; and detectingthe interference originating from lightning based on the demodulatedresulting signal.
 12. The method of claim 11, comprising arranging afrequency modulation demodulator and a lightning detection block inparallel.
 13. The method of claim 12, wherein the lightning detectionblock is placed after a down-conversion mixer and before the limiterstage in frequency modulation radio receiver.
 14. The method of claim11, comprising: defining an intermediate output after down-mixer in thefrequency modulation radio receiver; and using an empty frequencymodulation channel for lightning detection.
 15. The method of claim 11,comprising receiving frequency modulation radio signals simultaneouslywith the lightning detection.
 16. The method of claim 11, comprisingusing an automatic gain control stage of a frequency modulation radioreceiver in the lightning detection.
 17. The method of claim 11,comprising using an in-phase and a quadrature branch in thetelecommunication radio receiver for providing the triggering mode. 18.The method of claim 17, comprising using different local oscillatorfrequencies in the in-phase and the quadrature branch.
 19. The method ofclaim 17, comprising using different branch gains in the in-phase andthe quadrature branch.
 20. The method of claim 11, wherein atelecommunication radio receiver comprises a radio frequencyidentification tag.
 21. The method of claim 17, comprising using thein-phase and the quadrature branches to detect lightning strikes whilethe frequency modulation radio receiver is receiving frequencymodulation radio signals.